Congestive Heart Failure (CHF) has been singled out as an emerging epidemic with an increase in prevalence and the size of the population at risk. Nonetheless, the epidemiology of CHF is poorly understood, and there is a need for community-based studies of the incidence, prevalence, survival, therapy, and time trends of the syndrome. In this application, the investigators propose to conduct systematic surveillance of CHF among residents, 35-84 years old, of the Minneapolis-St. Paul metropolitan area (population 2.45 million, 1995 estimate) in two complementary domains: 1) hospitalization for CHF in two calendar years, five years apart (1995 and the year 2000); and 2) newly diagnosed CHF over 9-year period (1993-2001) among members of a large Health Maintenance Organization (HMO). The magnitude and characteristics of hospitalized CHF will be assessed in all acute care hospitals of the metropolitan area (N=21). One-third of all discharges with ICD-9 CHF codes will be sampled randomly (n about 5,000 per surveillance year), abstracted by trained nurses, and classified according to clinical criteria and the results of diagnostic tests. Newly diagnosed CHF will be distinguished from recurrent episodes of decompensated CHF by thorough review of the hospital record. A complementary perspective on CHF, including the outpatient setting, will be provided by a systematic study of members of HealthPartners, one of the largest HMOs in Minneapolis-St. Paul. Using the HealthPartners database, all newly diagnosed CHF cases between January 1, 1993 and December 31, 2001 (n about 1,900) will be identified and the diagnosis validated. Beginning in January 1, 1999, newly diagnosed CHF cases will be identified on an ongoing bases (n about 600), surveyed by mail, and followed for one-year from the original diagnosis. Surveillance of the HealthPartners population will supplement hospital surveillance and will contribute data on incidence, prevalence, treatment, use of resources, and patient outcomes. Efforts to reduce the burden of CHF in the U.S. will benefit from community-based data on the epidemiology of CHF. The investigators point out that the results of the proposed surveillance will provide guidance to public health decisions, broader surveillance projects of CHF, and a sensitive gauge of the success of medical efforts.